Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$22.45	12.173%	$25.1828	$25.18	$25.20	$25.20
Purchase #2	$64.99	12.133%	$72.8752	$72.88	$72.90	$72.90
Purchase #3	$102.44	13.462%	$116.2305	$116.23	$116.25	$116.20
Purchase #4	$34.64	8.521%	$37.5917	$37.59	$37.60	$37.60
Purchase #5	$153.99	10.112%	$169.5615	$169.56	$169.55	$169.60
Purchase #6	$128.32	13.181%	$145.2339	$145.23	$145.25	$145.20
Purchase #7	$50.27	7.499%	$54.0397	$54.04	$54.05	$54.00
7 purchase totals =	$557.10		$620.7153	$620.71	$620.80	$620.70